No effectively functioning separation plant has been available until now for the separation of certain types of impurity particles and sediment, etc., from water in the basins used for special fish breeding. A customary type of plant utilizes rotating filter drums, in which problems with the clogging of the filter surface are encountered, however, in spite of the continuous cleaning of the perforations in the surface of the filter. Belt filters with an endless filter belt running over two rollers are also subject to clogging, unless special measures are taken to prevent this.